1. Field of the Invention
The present invention relates to organic compounds, anthracene derivatives, and light-emitting elements, light-emitting devices, and electronic devices in which the anthracene derivatives are used.
2. Description of the Related Art
In a light-emitting element, a layer containing an organic compound is interposed between a pair of electrodes. Such a light-emitting element is characterized in that a thin and lightweight element can be fabricated, light is emitted by supply of direct current, response is faster compared to liquid crystals, and the like. Moreover, light-emitting devices in which such light-emitting elements are arranged in matrix form, that is, passive matrix light-emitting devices and active matrix light-emitting devices are superior to conventional liquid crystal displays in terms of wide viewing angle and high visibility. From such reasons, light-emitting elements are desired to be applied to next-generation flat panel displays. In some cases, light-emitting elements are referred to as electroluminescent elements or EL elements.
Electrons are injected from a cathode into a layer containing an organic compound interposed between a pair of electrodes, and at the same time, holes are injected from an anode into the layer containing an organic compound, whereby a light-emitting element is driven. The electrons injected from the cathode and the holes injected from the anode are recombined with each other in the layer containing an organic compound to form molecular excitons. The molecular excitons release energy in returning to a ground state. When the energy is released as light having a wavelength corresponding to that of visible light, light emission can be seen. Excited states of organic compounds include a singlet state and a triplet state, and when either state is the excited state, light can be emitted.
An emission wavelength of a light-emitting element is determined by the energy gap between a ground state and an excited state formed by the recombination, that is, a band gap. Therefore, a structure of a molecule that serves for emitting light is selected or modified as appropriate, whereby any emission color of light can be obtained. Further, full color light-emitting device can be manufactured when light-emitting elements that are capable of emitting light of red, blue, and green that are three primary colors of light are used for the manufacture of the light-emitting device.
In order to manufacture a full color light-emitting device with excellent color reproducibility, red, blue, and green light-emitting elements that are highly reliable and excellent in color purity are needed. As a result of recent developments of materials, high reliability and excellent color purity for red and green light-emitting elements have been achieved. However, enough efficiency and color purity for a blue light-emitting element have not been achieved. For example, in Nonpatent Document 1 (J. Shi et al., Applied Physics Letters, Vol. 80, No. 17, pp. 3201-3203, 2002), a blue light-emitting element with relatively high reliability is reported. For the light-emitting element, however, enough emission efficiency and color is not achieved.